Magnetoelectric machine



y 1949- 1 H. SCOTT 2,469,133

MAGNETO ELECTRIC MACHINE Filed NOV. 1, 1945 23 G 22 o 0 if I Z a 4INVENTOR:

Z759. 2 5. [Aw 17 A. 60077" Patented May 3, I949 MAGNETOELECTRIC MACHINELloyd B. Scott, Garden City, N. Y., asslgnor, by mesne assignments, toJack & Heintz Precision Industries, Inc., Cleveland, Ohio, a corporationof Delaware Application November 1, 1945, Serial No. 636,122

7 Claims. (Cl. 171-209) I This invention relates to electric generatorsand has particular reference to reversing flux type generators such asmagnetos, although the invention is is not limited to that use.

It is well known that in electric generators in which the voltagechanges alternately, unwanted impulses occur that may cause improperoperation of apparatus energized or otherwise actuated by the generatoroutput. In low tension generators, these unwantedimpulses, althoughundesirable and therefore to be minimized or eliminated if possible,usually do not materially affect the operation of appurtenant apparatus,but in higher tension generators, the sudden unwanted increase involtage or voltage increase at the wrong time may cause suchdiiliculties. For example, in engine ignition magnetos, such unwanted oruntimely voltage increases frequently result in the generation of anundesired spark across the spark plug gap irrespective of the operationof the breaker mechanism, thus causing improper operation of the engine,and, in the case of a single cylinder, two-cycle engine, such sparkingoccurs during the intake stroke and pre-ignition results. The phenomenonis particularly pronounced when the magneto is driven at relatively highspeed, when the resulting rapid changes of flux through the magneticcoil cause the regular generation of an untimely spark in the secondarywinding regardless of the operation of the breaker mechanism. Variousexpedients have been adopted to correct this condition, commonly knownas maverick sparkling, such as by distorting the pole shoes and thelike, and, whereas such expedients reduce maverick sparking they od noteliminate it, and usually result in increased cost of manufacture andcomplicated structures.

In accordance with the present invention, an electric generator of thereversing flux type is provided in which the generation of unwanted oruntimely voltage is minimized or eliminated, by modifying the wave formor amplitude of the voltage generated in the magnetic circuit so thatthe desired peak voltage only occurs at the proper point or time.

The invention comprises introducing into the magnetic circuit, includinga magnetic core and a coil, a short-circuited conductor such as a ringof conducting material encircling at least part of the magnetic circuitand having the property of damping the rate of flux change in the saidcircuit to the degree necessary to just allow establishment of maximumflux at the desired point in the cycle. In this way the wave form issimply and effectively modified to that desired in the generator,whether of the high or low tension type.

In the adaptation of the invention to'a ma neto, for example, thedamping ring is included in the magnetic circuit in such a way that therate of flux change prior to closing of the circuit breaker results inthe occurrence of the maximum flux at or close to the instant that thecircuit is closed, whereby the prior voltage is kept too low to induce apremature spark.

Thus, in a conventional form of flywheel magneto having the usualstationary core structure around which the field structure rotates withthe flywheel, the clampin device of this invention, either in the formof a closed ring or shortcircuited coil of conducting material likecopper, surrounds one leg of the core and thus encircles at least partof the magnetic circuit to perform the function described. Advantage maybe taken of the voltage induced in the coil by including in its closedcircuit one or more electric devices, such as incandescent lamps, forexample. In the other forms of magneto-electric generators, the dampingring is similarly placed in the magnetic circuit so as to encircle atleast part of the same to provide the degree of damping required.

It will be seen that the simple and inexpensive damping device of thisinvention efiectively modifies the rate of change of the flux in themagnetic circuit to a degree such that unwanted impulses do not occur orare suitably modified, the degree depending upon the proportion of themagnetic circuit that the device encircles and the amount of conductingmaterial comprising the device, which in turn depend upon the rate ofchange of flux desired in the magnetic circuit.

For a more complete understandin of the invention, reference may be hadto the accompanying drawings, in which:

Figure 1 illustrates the adaptation of the invention to a conventionalflywheel magneto structure, by way of illustration;

Figs. 2a and 2b are curves illustrating the modifying effect of theinvention on the rate of change of the flux and the voltage,respectively, in the generating coil magnetic circuit of the magneto ofFig. 1; and,

Fig. 3 is a fragmentary view of the core structure of Fig. 1, andillustrates a modification of the invention.

Referring to the drawings in which the invention is shown as adapted toa conventional flywheel magneto, the latter includes a fleld structurecarried by and rotating with the flywheel l anda stationary structure iicarrying the necessary coils, magnetic structure, breaker, etc. Thefield structure carried by the flywheel It may consist of'a circularpermanent magnet I! having the air gap II between its north and southpoles to which are attached the pole shoes II and II. The statorstructure ll carries laminations of iron or other magnetic materialformed with three legs, i8, i1 and II, which are united at their innerends and extend more or less radially with their outer ends angularlyspaced apart and curved to cooperate successively with the pole shoes I4and II on rotation of the field structure on the fiywheel it in thedirection of the arrow. The central leg I! of the core carries theprimary and secondary coils is and 2|, respectively.

The primary coil is is arranged in a circuit which can be opened andclosed by disengagement and engagement, respectively, of the cooperatingbreaker points 2! carried by the stator ii, one or which is mounted on alever 21 engaging a cam 23 rotating with the flywheel ii, and normallyurged against the cam 28 by the springs 24. The cam 23 normally holdsthe breaker points 2| open but allows the spring 24 to close them at atime when the leading pole shoe l overlaps the center leg I! and theother shoe H overlaps leg IS. The fiux established in one directionthrough the core is immediately followed by the building up of flux inan opposite direction through the core as the flywheel is rotated. Acondenser 25 carried by the stator II is bridged across the breakerpoints II, as is usual. The structure and magnetic circuit justdescribed are conventional and do not constitute the invention but serveto illustrate one type of magneto-electric machine to which theinvention is applicable.

As is well known with this type of magneto, th flux through the sparkcoil first rises from zero to a maximum value in one direction, thenreverses to a maximum value in the opposite direction, and finallyreturns to zero again as the flywheel is rotated with the contact pointsheld open and no damping means provided. When the cam is allowed to openand close the breaker mechanism, the flux rises from zero to a maximumas before, since the contact points are held open until the maximumvalue has been reached, such as point A on the flux curve of Fig. 2a. Atthis point A the contacts close, thus completing the primary circuit andpreventing the normal reversal of fiux through generation of primarycurrent until point B is reached, when the contacts open, allowing theflux to change very rapidly from point B to point C. This induces a highvoltage surge in the secondary winding, as indicated at point G on thevoltage curve shown by Fig. 2b, which produces the desired spark at thespark plug in the engine. Since the original increase of flux from zeroto maxi mum also links the secondary wind ng of the coil, this change offiux also induces a peak of voltage proportional to the maximum rate ofchange of flux at this time, which is indicated at point D on Fig. 2a.At high rotat'ive speeds, the rate of change of flux at point D becomessufiicient 1y great to induce in the secondary winding a high peakvoltage value, as indicated at point F on the voltage curve of Fig. 2b.This peak voltage may be sufilcient to cause a spark to jump at thespark plug in the engine, thus producing the so-called maverick or earlyignition discharge.

In order to so reduce the voltage at point F of Fig. 2b that a maverickspark is not produced at the spark plug, it is necessary to reduce therate of change of the flux build-up indicated at point D of Fig. 2a.This is accomplished in accordance with the invention by encircling theleading leg of the stator core with a dampin coil or ring. The currentsgenerated in this ring oppose the rapid change of flux and by properproportioning of the ring, the flux curve may be made to approach thatshown by the dotted line E in Fig. 2a, which is accompanied by a greatreduction in the peak value of the maverick voltage generated, as isindicated by dotted curve H in Fig. 2b. This damping coil or ring doesnot materially aflect the performance or the desired spark, occurring atpoint 0 of Fig. 2b, since the leading leg of the core is not included inthe operating circuit of the magneto at the time the contact pointsopen. The device may consist simply of a copper strip encircling the legI, as shown in Fig. 1. Other conducting materials may be used instead ofcopper if desired, such as silver, 'brass, aluminum, etc. The weight ofthe conducting material is determined by experiment as it depends uponthe degree of Supp e s o 0 inclination of the dotted line slope E inFig. 2a that is desired.

Operation of the damping device of this invention will be readilyunderstood from the foregoing, the ring 2t encircling at least part ofthe magnetic circuit serving as a means for controlling or modifying therate of change of the fiux in the magnetic circuit, with the eflectindicated by way of example in Fig. 2a, which in magnetos has theadvantage of supressing or eliminating maverick sparking.

Instead of a single turn coil or ring 26, a shortcircuited coil,consisting of copper or other conducting wire with its ends soldered orotherwise electrically connected together may be used with equalfacility. Because such a winding has a voltage induced therein, thisvoltage may be conveniently utilized to illuminate an incandescent lampor for other purposes for which the surplus energy available is desired.Such an arrangement is indicated schematically in Fig. 3, wherein thecoil 28 is short-clrcuited through the lamp 21 which accordingly glowswhen the magneto is in operation by reason or the voltage induced in the001128.

Although a preferred embodiment of the invention has been illustratedand described herein. it is to be understood that the invention is notlimited thereby but is susceptible of changes in form and detail withinthe scope of the appended claims.

I claim:

1. In a magneto for use in connection with internal combustion engineignition systems, or the like, having spark plugs, or the like, withspark gaps, said magneto having a magnetic circuit including a magnetand pole shoe structure and a. relatively rotatable magnetic corestructure having spaced arms intermittently bridged thereby, said corestructure including primary and secondary windings on one of said arms,a circuit breaker for said primary winding for releasing a spark fromthe secondary winding across said gap, a member of conducting materialof predetermined proportions mounted on said core and encircling apredetermined portion of said magnetic circuit for predeterminedlymodifying the rate of change of the iiux traversing the same to anextent sufllcient for precluding premature sparking across said gap.

2. In a magneto for use in connection with internal combustion engineignition systems, or

the like, having spark plugs, or the like, with spark gaps, said magnetohaving a magnetic circuit including a magnet and pole shoe structure anda relatively rotatable magnetic core structure having spaced armsintermittently bridged thereby, said core structure including primaryand secondary windings on one of said arms, a circuit breaker for saidprimary windings for releasing a spark from the secondary winding acrosssaid gap, a member of conducting material of predetermined proportionsmounted on said core and encircling another of said core arms forpredeterminedly modifying the rate of change of the flux traversing thesame to an extent suiilcient for precluding premature sparking acrosssaid gap.

3. In a magneto for use in connection with internal combustion engineignition systems, or the like, having spark plugs, or the like, withspark gape, said magneto having a magnetic circuit including a magnetand pole shoe structure and a relatively rotatable magnetic corestructure having spaced arms intermittently bridged thereby, said corestructure including primary and secondary windings on one of said arms,a circuit breaker for said primary winding for releasing a spark fromthe secondary winding across said gap, a coil of conducting material ofpredetermined proportions mounted on said core and encircling another ofsaid core arms for predeterminedly modifying the rate of change of theflux traversing the same to an extent sufiicient for precludingpremature sparking across said gap.

4. In a magneto for use in connection with internal combustion engineignition systems, or the like, having spark plugs, or the like, withspark gaps, said magneto having a magnetic circuit including a magnetand pole shoe structure and a relatively rotatable magnetic corestructure having spaced arms intermittently bridged thereby, said corestructure including primary and secondary windings on one of said arms,a circuit breaker for said primary winding for releasing a spark fromthe secondary winding across said gap, a short-circuited coil ofconducting material of predetermined proportions mounted on said coreand encircling another of said core arms for predeterminedly modifyingthe rate of change of the flux traversing the same to an extentsuihcient for precluding premature sparking across said gap.

5. In a magneto for use in connection with internal combustion engineignition systems, or the like, having spark plugs, or the like, withspark gaps, said magneto having a magnetic circuit including a magnetand pole shoe structure and a. relatively rotatable magnetic corestructure having spaced arms intermittently bridged thereby, said corestructure including primary and secondary windings on one of said arms,a circuit breaker for said primary winding for releasing a spark fromthe secondary winding across said gap, a short-circuited coil ofconducting material of predetermined proportions having its endselectrically connected and mounted on said cor and encircling another ofsaid core arms for predeterminedly modifying the rate of change of theflux traversing the same to an extent suflicient for precludingpremature sparking across said gap.

6. In a magneto for use in connection with internal combustion engineignition systems, or the like, having spark plugs, or the like, withspark gaps, said magneto having a magnetic circuit including a magnetand pole shoe structure and a relatively rotatable magnetic corestructure having spaced arms intermittently bridged thereby, said corestructure including primary and secondary windings on one of said arms,a circuit breaker for said primary winding for releasing a spark fromthe secondary winding across said gap, a member of conducting materialof predetermined proportions mounted on said core and encircling anotherof said core arms in advance of said arm carrying said primary andsecondary windings for predeterminedly modifying the rate of change ofthe flux traversing the same to an extent suillcient for precludingpremature sparking across said gap.

'7. In a magneto for use in connection with internal combustion engineignition systems, or the like, having spark plugs, or the like, withspark gaps, said magneto having a magnetic circuit including a magnetand pole shoe structure and a relatively rotatable magnetic corestructure having spaced arms intermittently bridged thereby, said corestructure including primary and secondary windings on one of said arms,a circuit breaker for said primary winding for releasing a spark fromthe secondary winding across said gap, a short circuited coil ofconducting material of predetermined proportions mounted on said coreand encircling another of said core arms in advance of said core armcarrying said primary and secondary windings i'or predeterminedlymodifying the rate of change of the flux traversing the same to anextent sufficient for precluding premature sparking across said gap.

LLOYD H. SCO'I'I.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,331,998 Neuland Feb. 24, 19201,970,338 Roebel Aug. 14, 1934 2,128,044 Grabner Aug. 23, 1938 FOREIGNPATENTS Number Country Date 742,751 France Sept. 12, 1932

